Exhaust aftertreatment system

ABSTRACT

In one exemplary embodiment of an exhaust aftertreatment system, the system includes an oxidation catalyst configured to receive an exhaust gas flow from an internal combustion engine and a particulate filter positioned downstream of the oxidation catalyst, the particulate filter comprising a substrate. The system also includes a nitrogen oxide adsorbing catalyst applied to a downstream portion of the substrate and a selective catalytic reduction device positioned downstream of the nitrogen oxide adsorbing catalyst, wherein the selective catalytic reduction device is configured to remove nitrogen oxides from the exhaust gas flow.

FIELD OF THE INVENTION

The subject invention relates to internal combustion engines, and, moreparticularly, to exhaust aftertreatment systems for internal combustionengines.

BACKGROUND

An engine control module of an internal combustion engine controls themixture of fuel and air supplied to combustion chambers of the engine.After the air/fuel mixture is ignited, combustion takes place and thecombustion gases exit the combustion chambers through exhaust valves.The combustion gases are directed by an exhaust manifold to a catalyst(or “catalytic converter”) and/or other exhaust aftertreatment systems.

During certain engine operating conditions combustion gases may enterthe exhaust system while components of the aftertreatment system, suchas the catalyst, are not yet heated to operating temperatures at whichthey can adequately reduce regulated exhaust gas constituents. The issueis typically greatest following a cold engine startup. Cold exhaustsystem components can have large thermal masses that act as heat sinks,thereby slowing down heating of the exhaust system and the catalystscontained therein. Therefore, following startup, a slow temperature risein exhaust system components can lead to undesirable emission levels,due to the corresponding slow response and light-off (i.e. activation)of the catalyst(s).

SUMMARY OF THE INVENTION

In one exemplary embodiment of the invention, an exhaust aftertreatmentsystem includes an oxidation catalyst configured to receive an exhaustgas flow from an internal combustion engine and a particulate filterpositioned downstream of the oxidation catalyst, the particulate filtercomprising a substrate. The system also includes a nitrogen oxideadsorbing catalyst applied to a downstream portion of the substrate anda selective catalytic reduction device positioned downstream of thenitrogen oxide adsorbing catalyst, wherein the selective catalyticreduction device is configured to remove nitrogen oxides from theexhaust gas flow.

In another exemplary embodiment of the invention, an internal combustionengine includes an oxidation catalyst in fluid communication with anexhaust manifold and a particulate filter configured to receive anexhaust gas flow from the oxidation catalyst. The internal combustionengine also includes a nitrogen oxide adsorbing catalyst configured toreceive the exhaust flow from the particulate filter and a selectivecatalytic reduction device configured to receive the exhaust flow fromthe nitrogen oxide adsorbing catalyst, wherein the configuration of thenitrogen oxides catalyst and the selective catalytic reduction catalystenable adsorption of nitrogen oxides by the nitrogen oxide adsorbingcatalyst during a start up period, release of the nitrogen oxides afterthe start up period and removal the nitrogen oxides from the exhaustflow by the selective catalytic reduction catalyst as the nitrogenoxides are released by the nitrogen oxide adsorbing catalyst.

The above features and advantages and other features and advantages ofthe invention are readily apparent from the following detaileddescription of the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and details appear, by way of example only,in the following detailed description of embodiments, the detaileddescription referring to the drawings in which

FIG. 1 illustrates an exemplary schematic view of an internal combustionengine including an exemplary exhaust aftertreatment system; and

FIG. 2 is a perspective view of a portion of the exemplary exhaustaftertreatment system of FIG. 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is notintended to limit the present disclosure, its application or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

FIG. 1 is a schematic diagram of an embodiment of an engine system 100.The engine system 100 includes an internal combustion engine 102, anexhaust system 104 and an engine controller 106. The exhaust system 104includes an exhaust manifold 108, an exhaust aftertreatment system 110and an exhaust conduit 112. Cylinders 116 are located in the internalcombustion engine 102, wherein the cylinders 116 receive a combinationof combustion air and fuel. The combustion air/fuel mixture is combustedresulting in reciprocation of pistons (not shown) located in thecylinders 116. The reciprocation of the pistons rotates a crankshaft(not shown) to deliver motive power to a vehicle powertrain (not shown)or to a generator or other stationary recipient of such power (notshown) in the case of a stationary application of the internalcombustion engine 102. The combustion of the air/fuel mixture causes aflow of exhaust gas 118 through the exhaust manifold 108 and into theexhaust gas aftertreatment system 110, wherein the exhaustaftertreatment system 110 may include an oxidation catalyst 119, aparticulate filter 120, a nitrogen oxide adsorbing catalyst (“NAC”) 122and a selective catalytic reduction (“SCR”) device 124. The exhaustaftertreatment system 110 reduces, oxidizes, traps or otherwise treatsvarious regulated constituents of the exhaust gas 118, such as nitrogenoxides (“NOx”), carbon monoxide (“CO”), hydrocarbon (“HC”) andparticulates prior to its release to the atmosphere.

In addition, the exhaust aftertreatment system 110 and a fluid supply125 are operationally coupled to and controlled by engine controller106. The engine controller 106 collects information regarding theoperation of the internal combustion engine 102 from sensors 128 a-128n, such as temperature (intake system, exhaust system, engine coolant,ambient, etc.), pressure, exhaust flow rates, NOx concentrations and, asa result, may adjust the amount of an emission reducing fluid, such asurea or ammonia gas, injected into the exhaust aftertreatment system110. As used herein the term controller refers to an applicationspecific integrated circuit (ASIC), an electronic circuit, a processor(shared, dedicated or group) and memory that executes one or moresoftware or firmware programs, a combinational logic circuit, and/orother suitable components that provide the described functionality. Inan exemplary embodiment, the exhaust gas flow 118 is received by theoxidation catalyst 119, which may be closely-coupled, to the engineexhaust manifold to minimize heat loss. The particulate filter 120 isconfigured to remove particulate matter or soot from the exhaust gasflow 118. In an embodiment, the NAC 122 may be a NOx absorbing coatingapplied to a downstream portion of the particulate filter 120 substrate,where the NAC 122 adsorbs NOx at a first temperature and releases NOx ata second temperature. The first temperature is lower than a thresholdand the second temperature is higher than the threshold. After the NOxis released at the second temperature by the NAC, the SCR device 124receives the exhaust gas 118 and is sufficiently heated to remove NOxfrom the exhaust. In an embodiment, the SCR device 124 simultaneouslyremoves NOx from the exhaust gas flow 118 as the NAC 122 releases theNOx.

With continuing reference to FIG. 1, during a startup period for theexemplary internal combustion engine system 102, components of theexhaust aftertreatment system 110, such as the SCR device 124, arerelatively “cool” and can take time to be warmed up to an operatingtemperature. Specifically, when heated to its operating temperature, theSCR device 124 removes NOx more effectively from the exhaust gas flow118. Accordingly, a method and apparatus are provided for the exhaustaftertreatment system 110 to enable the SCR device 124 to remove NOxfrom the exhaust gas flow 118 after being heated at or above a thresholdoperating temperature, thereby reducing emissions. As discussed herein,the operating temperature for the SCR device 124 is a temperature orrange of temperatures where the device is able to remove a sufficientamount of NOx, to achieve selected targets.

FIG. 2 is a perspective view of a portion of the exemplary exhaustaftertreatment system 110. As depicted, the exhaust aftertreatmentsystem 110 receives the exhaust gas flow 118 into the oxidation catalyst119, which may be a diesel oxidation catalyst (DOC). The Exhaust gasflows into the particulate filter 120, which may be a diesel particulatefilter. The oxidation catalyst 119 is configured to oxidize selectedpollutants, such as carbon monoxide and hydrocarbon, from the exhaustgas flow 118, while the particulate filter 120 is configured to removesoot and other particulates. In an embodiment, the NAC 122 is downstreamof the particulate filter 120 and is configured to adsorb or capture NOxfrom the exhaust gas flow 118 at a first temperature. Further, the NAC122 is also configured to release the adsorbed NOx at a secondtemperature that is higher than the first temperature. The exemplary NAC122 is a coating of suitable material applied to a downstream portion ofa substrate of the particulate filter 120. Exemplary materials for thecoating include, but are not limited to, basic metal oxides (γ-Al₂O₃,CeO₂, MgO, MgO/Al₂O₃, BaO/Al₂O₃, K₂O/Al₂O₃) and metal exchanged zeolites(Na-exchanged and Ba-exchanged faujasite, such as NaY and BaY, as wellas Cu-exchanged and Fe-exchanged Beta). As depicted, an assembly 200allowing close coupling to the engine exhaust manifold 108 includes theoxidation catalyst 119, the particulate filter 120 and the NAC 122. Asdiscussed herein, close coupled components are close in proximity to anexhaust exit of the internal combustion engine 102 to reduce a length ofat least a portion of an exhaust gas flow path. Further, close coupledcomponents are placed substantially adjacent or proximate one another tocause a reduced exhaust flow path between components. Close coupledcomponents reduce thermal degradation (i.e., heat loss) caused byexhaust gas flow along longer flow paths and resultant thermal mass and,accordingly, provide more rapid heating of components to operatingtemperatures due to shorter overall flow paths. In other embodiments,the oxidation catalyst 119, the particulate filter 120 and the NAC 122are separate components, wherein the NAC 122 is applied to a substratedownstream of, and separate from, the particulate filter 120.

An emission fluid injector 202 is positioned downstream of the closecouple assembly 200 to inject an emission fluid, such as urea, to assistthe SCR device 124 in reduction of NOx constituents in the exhaust gasflow 118. A mixer may be located in an exhaust conduit 204 to improvedistribution and mixing of the emission fluid. The SCR device 124 isconfigured to receive the exhaust gas flow 118 mixed with emission fluidand reduce the NOx in the exhaust gas. After NOx and other exhaust gascomponents are removed, the exhaust gas 118 flows downstream to otheraftertreatment devices or into the atmosphere, depending on theapplication. The exemplary SCR device 124 is configured to remove NOxfrom exhaust at or above a threshold operating temperature, such asabout 150 degrees C. In other embodiments, the operating temperature isat or above about 175 degrees C. In yet other embodiments, the operatingtemperature is at or above about 200 degrees C. At lower exhaust flowrates, the temperature for initiating urea injection is about 150degrees C. At higher exhaust flow rates, the temperature for ureainjection is higher, such as about 175 to about 200 degrees C.

An exemplary start up period begins when a “cool” engine (i.e., notwarmed up) is started. In embodiments, certain components are notsufficiently heated to operate efficiently during the start up period.Specifically, the SCR device 124 may not remove NOx at a desired rate,such as to reduce levels to meet certain regulations or targets, duringthe start up period. Thus, in an embodiment, the NAC 122 is configuredto adsorb NOx from the exhaust gas flow 118 during the start up period.After the start up period, the NAC 122 is heated and can no longeradsorb NOx. In addition, after the start up period, the NAC 122 releasesthe adsorbed NOx pollutants for treatment by the SCR device 124, whereinthe SCR device 124 has been heated to an operating temperature to removeNOx. For example, following a cold startup, the SCR device 124 and theNAC 122 are substantially cool and the NAC 122 adsorbs NOx at or belowits “release” temperature. The release temperature is a temperature atwhich the NAC 122 slows or stops adsorbing NOx and begins to releaseadsorbed NOx. After the start up period, the NAC 122 and SCR device 124are above a threshold temperature (i.e., about equal to the releasetemperature of the NAC and the operating temperature of the SCR),wherein the NAC 122 releases the NOx and the SCR device 124 is heatedand able to remove NOx from the exhaust gas. In embodiments, the firsttemperature is below about 100 degrees C. and the second temperature isequal to or greater than about 150 degrees C. In the example, the NAC122 and SCR device 124 are heated from below about 100 degrees C. toabout 150 degrees C. during the start up period, wherein the componentsare at or above 150 degrees C. after the start up period.

The embodiments depicted in FIGS. 1 and 2 are configured tosubstantially “match” the temperatures of the NAC 122 and SCR device124, wherein NAC 122 and SCR device 124 are both heated by the exhaustgas to a selected temperature or threshold where the NAC 122 releasesNOx for removal by the SCR device 124 after the start up period. Inaddition, the depicted arrangement does not have a filter positionedbetween the NAC 122 and SCR device 124. Accordingly, the arrangementenables the temperature of the exhaust gas 118 flow to be substantiallymatched or similar at the NAC 122 and SCR device 124 by not havingdevices that act as heat sinks between the components. For example, theNAC 122 adsorbs NOx while the exhaust gas flow heats the NAC 122 and SCRdevice 124. The SCR device 124 then receives the released NOx fortreatment from the NAC 122 after the start up period, when thetemperatures of the NAC 122 and SCR device 124 are both heated andsubstantially matched to improve emissions reduction. Accordingly, thearrangement depicted in FIGS. 1 and 2 substantially matches thetemperatures of the NAC 122 and SCR device 124 to improve NOx reductionduring and after the engine's start up period.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiments disclosed, but that theinvention will include all embodiments falling within the scope of theapplication.

What is claimed is:
 1. An exhaust aftertreatment system, comprising: anoxidation catalyst configured to receive an exhaust gas flow from aninternal combustion engine; a particulate filter positioned downstreamof the oxidation catalyst, the particulate filter comprising asubstrate; a nitrogen oxide adsorbing catalyst applied to a downstreamportion of the substrate; and a selective catalytic reduction devicepositioned downstream of the nitrogen oxide adsorbing catalyst, whereinthe selective catalytic reduction device is configured to removenitrogen oxides from the exhaust gas flow.
 2. The exhaust aftertreatmentsystem of claim 1, wherein the nitrogen oxide adsorbing catalyst adsorbsnitrogen oxides below a threshold temperature during a start up periodfor the internal combustion engine and releases the nitrogen oxidesabove the threshold temperature, wherein the second temperature isgreater than the first temperature.
 3. The exhaust aftertreatment systemof claim 1, wherein the selective catalytic reduction device removesnitrogen oxides at an operating temperature that is greater than itstemperature following a start up period for the internal combustionengine.
 4. The exhaust aftertreatment system of claim 1, wherein atemperature of the exhaust gas flow is substantially matched between thenitrogen oxide adsorbing catalyst and the selective catalytic reductiondevice.
 5. The exhaust aftertreatment system of claim 1, wherein theconfiguration of the nitrogen oxide adsorbing catalyst and the selectivecatalytic reduction device enable adsorption of nitrogen oxides by thenitrogen oxide adsorbing catalyst during a start up period, release ofthe nitrogen oxides after the start up period and removal of thenitrogen oxides simultaneously by the selective catalytic reductiondevice from the exhaust gas flow as the nitrogen oxides are released bythe nitrogen oxide adsorbing catalyst.
 6. The exhaust aftertreatmentsystem of claim 1, comprising an emission fluid injector positioned in aflow path between the nitrogen oxide adsorbing catalyst and theselective catalytic reduction device.
 7. The exhaust aftertreatmentsystem of claim 1, wherein the oxidation catalyst and the particulatefilter are closely coupled to the internal combustion engine.
 8. Aninternal combustion engine comprising: an oxidation catalyst in fluidcommunication with an exhaust manifold; a particulate filter configuredto receive an exhaust gas flow from the oxidation catalyst; a nitrogenoxide adsorbing catalyst configured to receive the exhaust flow from theparticulate filter; and a selective catalytic reduction deviceconfigured to receive the exhaust flow from the nitrogen oxide adsorbingcatalyst, wherein the configuration of the nitrogen oxides catalyst andthe selective catalytic reduction catalyst enable adsorption of nitrogenoxides by the nitrogen oxide adsorbing catalyst during a start upperiod, release of the nitrogen oxides after the start up period andremoval the nitrogen oxides from the exhaust flow by the selectivecatalytic reduction catalyst as the nitrogen oxides are released by thenitrogen oxide adsorbing catalyst.
 9. The internal combustion engine ofclaim 8, wherein the nitrogen oxide adsorbing catalyst adsorbs nitrogenoxides below a threshold temperature during a start up period for theinternal combustion engine and releases the nitrogen oxides after thestart up period above the threshold temperature.
 10. The internalcombustion engine of claim 8, wherein the selective catalytic reductiondevice removes nitrogen oxides at an operating temperature that isgreater than its temperature during the start up period.
 11. Theinternal combustion engine of claim 8, wherein a temperature of theexhaust gas flow is substantially matched between the nitrogen oxideadsorbing catalyst and the selective catalytic reduction device.
 12. Theinternal combustion engine of claim 8, comprising an emission fluidinjector positioned in a flow path between the nitrogen oxide adsorbingcatalyst and the selective catalytic reduction device.
 13. The internalcombustion engine of claim 8, wherein the oxidation catalyst, theparticulate filter and the nitrogen oxide adsorbing catalyst are closelycoupled to the internal combustion engine.
 14. An exhaust aftertreatmentsystem, comprising: an oxidation catalyst configured to receive anexhaust gas flow from an internal combustion engine; a particulatefilter configured to receive an exhaust gas flow from the oxidationcatalyst; a nitrogen oxide adsorbing catalyst configured to receive theexhaust flow from the particulate filter; and a selective catalyticreduction device configured to remove nitrogen oxides from the exhaustgas flow received from the nitrogen oxide adsorbing catalyst, wherein atemperature of the exhaust gas flow is substantially matched between thenitrogen oxide adsorbing catalyst and the selective catalytic reductiondevice.
 15. The exhaust aftertreatment system of claim 14, wherein thenitrogen oxide adsorbing catalyst adsorbs nitrogen oxides below athreshold temperature during a start up period for the internalcombustion engine and releases the nitrogen oxides above the thresholdtemperature.
 16. The exhaust aftertreatment system of claim 15, whereinthe selective catalytic reduction device removes nitrogen oxides atabout the second temperature.
 17. The exhaust aftertreatment system ofclaim 14, wherein the configuration of the nitrogen oxide adsorbingcatalyst and the selective catalytic reduction device enable adsorptionof nitrogen oxides by the nitrogen oxide adsorbing catalyst during astart up period of the internal combustion engine, release of thenitrogen oxides after the start up period and removal of the nitrogenoxides from the exhaust flow as the nitrogen oxides are released by thenitrogen oxide adsorbing catalyst.
 18. The exhaust aftertreatment systemof claim 14, comprising an emission fluid injector positioned in a flowpath between the nitrogen oxide adsorbing catalyst and the selectivecatalytic reduction device.
 19. The exhaust aftertreatment system ofclaim 14, wherein the nitrogen oxide adsorbing catalyst is applied to adownstream portion of a substrate of the particulate filter.
 20. Theexhaust aftertreatment system of claim 19, wherein the oxidationcatalyst and the particulate filter are closely coupled to the internalcombustion engine.